The present invention relates to a metalorganic chemical vapor deposition method for depositing an F-series metal (i.e., elements having an atomic number of 57 through 71 and 89 through 103) onto a semiconductor or other substrate, a metalorganic chemical vapor deposition method for incorporating nitrogen as a p-type dopant in Group II-VI semiconductor materials, metal amide compositions which can be used in metalorganic chemical vapor deposition as the source compound for an F-series metal or nitrogen, and to methods for preparing the metal amide compositions.
Generally, chemical vapor deposition (CVD) involves producing a reactant gas by contacting a volatile source compound for the material to be grown with a carrier gas. The reactant gas is introduced into a heated reactor chamber of an epitaxial reactor system that contains a substrate supported by a susceptor. Upon thermal decomposition of the source compound contained in the reactant gas, the desired component of the reactant gas is condensed from the vapor phase and grows epitaxially on the substrate. When a metalorganic composition is used as a source compound in CVD, the method is properly called organometallic vapor phase epitaxy (OMVPE) or metalorganic chemical vapor deposition (MOCVD). CVD offers several advantages over competing epitaxy methods such as molecular beam epitaxy (MBE), including: (1) the ability to grow relatively large surface area materials; (2) higher throughput and (3) lower equipment costs.
MOCVD is widely used for the epitaxial growth of semiconductor materials used in the electronics industry. A common disadvantage of semiconductor materials is a temperature dependent energy gap between the electron valence and conduction bands. This drawback limits the performance of electroluminescent and optoelectronic semiconductor components which utilize the energy released upon transition of a promoted electron from the conduction band to a "hole" in the valence band (e.g., LED's, diode lasers, etc.). One solution to this problem is to incorporate a dopant into the semiconductor material which provides a pathway for election transitions from the conduction band to lower energy states that subsequently produces an essentially temperature independent energy emission. In order to serve as an effective dopant for this purpose, an element must have electron orbital transitions within the appropriate energy range for the semiconductor material and should be essentially free of competing energy transitions.
F-series metals have accessible f--f electron orbital transitions which fall within the appropriate energy range for a variety of semiconductor materials, including Group III-V (e.g., GaAs, AlGaAs); Group II-VI (e.g., ZnSe, CdS); and Group IV (e.g., Si, SiC, SiGe) semiconductors. Thus, F-series metals are suitable dopants to incorporate in these various semiconductor materials to reduce the effects of a temperature dependent band gap on semiconductor performance. "Rare Earth Doped Semiconductors", Symposium held April 13-15, 1993, San Francisco, Calif., Materials Research Society Symposium Proceedings, Vol. 301 (1993). Diode lasers made from stable, erbium-doped GaAs and AlGaAs are of particular importance because their 1538 nm wavelength matches that needed for efficient pumping of erbium-doped fibers used in optical amplifiers.
Group II-VI semiconductor materials such as zinc selenide (ZnSe) and cadmium sulfide (CdS) which contain a p-n junction may be used in optoelectronic devices that function in the blue region of the visible spectrum such as blue lasers, blue LED's and blue emission devices both active and passive. However, introducing p-type dopants into the Group II-VI lattice system has proven to be problematic. Marginal success has been achieved incorporating lithium as a p-type dopant at the Zn lattice site of ZnSe grown by MOCVD using Zn(CH.sub.3).sub.2 and Se(CH.sub.3).sub.2 as the Group II-VI element source compounds and tertiary-butyllithium or cyclopentadienyl lithium as the lithium source compound. Also, bis-bis-(trimethylsilyl) zinc amide has been used in MOCVD as a nitrogen source compound in depositing a nitrogen-doped ZnSe epitaxial layer using Zn(C.sub.2 H.sub.5).sub.2 and H.sub.2 Se as the Group II-VI element source compounds. Rees et al. "Evaluation of Zn {N[Si(CH.sub.3).sub.3 ].sub.2 }.sub.2 as a p-type Dopant in OMVPE Growth of ZnSe", Journal of Electronic Materials, Vol. 21 No. 6, pp. 361-366, (1992). Although bis-bis-(trimethylsilyl) zinc amide proved to be an adequate source compound for nitrogen doping of ZnSe, the effectiveness of the MOCVD process could be improved by utilizing a nitrogen source compound exhibiting a more consistent vapor pressure and cleaner decomposition kinetics so that fewer contaminants are left behind. Furthermore bis-bis-(trimethylsilyl) zinc amide can be difficult to purify for use in MOCVD and may be unstable at some MOCVD operating conditions.